A gas-solid fluidized bed bioreactor was successfully used to treat air contaminated with a volatile organic compound (VOC). A bioreactor containing both a fluidized and packed bed of moist peat granules removed ethanol, a representative VOC, from an air stream. The fluidized bed operation mode of the bioreactor outperformed the packed bed mode. The maximum elimination capacity (EC) of ethanol in the fluidized mode was 1520 g m(-3) h(-1), with removal efficiencies ranging between 45 and 100%, at loadings up to 3400 g m(-3) h(-1). Maximum EC was 530 g m(-3) h(-1) in the packed bed mode. Removal efficiency in the fluidized bioreactor was best at the lowest velocity, where the bubbling bed fluidization regime predominated. As gas velocity increased, the size and amount of large bubbles (slugs) increased and removal efficiency decreased while elimination capacity increased. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.